What do they do? Are they just floating around?
In: 6
They don’t do much of anything, but they do balance the books in some kinds of fusion reactions and particle decay.
Fusion in stars destroys protons and electrons to make neutrons, there’s a physical law that says you get one electron neutrino in exchange for every electron destroyed. Beta decay creates electron-proton pairs from neutrons and kicks off anti-neutrinos.
If you have a really, really high neutrino or antineutrino flux it’s possible to observe them pushing those reactions backwards. The [Cowan-Reines](https://en.wikipedia.org/wiki/Cowan%E2%80%93Reines_neutrino_experiment) experiment used antineutrinos to make positrons. (Positrons don’t last very long but the annihilation reaction with electrons generates a distinctive gamma ray.)
This means they certainly play a meaningful role in supernovae and supernovae are needed to make any element heavier than iron, so they’re essential even though they can be ignored in pretty much every normal situation.
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